For basic shapes, use the shape drawing tool. Even click once to enter exact measurments.
Or draw your shape using the pen tool, a great tool for measuring can be found at Nineblock. These guys have come up with a plug-in that can measure vectors. If you are going to use it for drafting and pattern design in your already familiar Adobe Illustrator interface it is well worth the license cost.
Create smooth arcs easily with the pen tool once the straight foundation lines are made. The Great thing is the copy and paste feature, for instance make a pleated shape once and then cut and paste for the desired effect, alot easier than measuring out and drawing on paper.
Anyway, if you have a good working knowledge of pattern drafting the "old school" way and learn illustrator you can really get creative.
Here is a simple pattern I made to show how using the offset path tool can easily define the finished panel shape and needed seam allowance. Always keep your pattern in Inch by Inch Real size so you can choose the right offset=seam allowance. in this case 1/4" because it is for a small felt toy. (I made 10 of these out of multi colored felt for a plush campfire scene.)
